The invention relates to a module provided with a thin-film circuit on a substrate of an insulating material, a method of manufacturing a module with a thin-film circuit, and a thin-film circuit.
The development of numerous electronic devices is characterized by the following trends: miniaturization, lower or at least constant prices accompanied by an enhanced functionality, higher reliability, and a lower energy consumption. Experience has shown that the number of passive components accounts for 70% of the number of components present in many consumer electronics appliances, for example in TV sets or video recorders. But it is also the stormy developments in the field of mobile telephony and the continuing miniaturization of the cordless telephone appliances which lead to higher requirements being imposed on the individual components.
A step on the road to a continuing miniaturization is provided by the so-called SMD technique. This technique is based on miniaturized components (SMDs=Surface Mounted Devices) which are directly mounted on the surfaces of printed circuit boards or ceramic substrates provided with conductor strips. SMDs are substantially smaller than corresponding components with traditional wiring. If used consistently, the surface or space requirements and the weight of circuits can be reduced by a factor two or three. It is also possible through an optimum application of the SMD technique to achieve a cost saving, because smaller printed circuit boards can be used.
A power amplifier module for the high-frequency unit of a mobile telephone is also manufactured by this technique nowadays. Conductor strips are provided on a substrate in a printing process. The substrate serves as a carrier for active components such as, for example, amplifiers, and passive components such as, for example, resistors, capacitors, and inductors. The active components are in that case fastened in the form of ICs by a bonding method, and the passive components are soldered thereon as SMD components.
A further miniaturization, however, also renders the manufacture, handling, and mounting of passive SMD components increasingly difficult. This can be avoided in that integrated passive components (IPCs) are used. In this technique, passive components such as, for example, resistors (R), capacitors (C), or inductors (L) are combined into inseparable basic circuits and systems. So-called thin-film circuits are obtained through the use of thin-film techniques by means of masks on carrier plates made of an insulating material, which circuits are the equivalents of very strongly reduced printed circuits. The manufacture of thin-film circuits is known and is generally achieved by means of several consecutive coating and structuring processes. Several layers of various shapes, compositions, and thicknesses are to be provided in order to realize a thin-film circuit, which consists of a combination of resistors, capacitors, and/or inductors.
A simple realization of circuits with widely differing passive and active components is possible through a combination of discrete (SMD) components with active components which have a special function (for example, a filtering function). A disadvantage is, however, that SMD components all have to be soldered individually. Large surface areas are required on account of the solder spots, which makes the circuits very bulky.
The invention has for its object to provide a module with a thin-film circuit comprising passive components or comprising passive and active components on a substrate of an insulating material which requires only little space.
This object is achieved by means of a module provided with a thin-film circuit on a substrate of an insulating material with at least one passive element, which element comprises at least
a first structured electrically conducting layer,
a dielectric, and
a second electrically conducting layer,
and with a protective layer,
as well as at least one contact hole which passes through the module, and a metallization which covers the module and the contact hole.
Not only the conductor strips, but also at least one passive element such as, for example, a capacitor is provided on a substrate in this thin-film circuit. This direct integration of passive elements renders it possible to realize the entire thin-film circuit with a substantially reduced space requirement.
In a particularly preferred embodiment, a resistance layer is provided between the substrate and the first structured electrically conducting layer, such that the thin-film circuit comprises at least one resistor.
It is preferred that the substrate of insulating material comprises a ceramic material, a glass-ceramic material, a glass material, or a ceramic material with a planarizing layer of glass or of an organic material.
A substrate made of these materials can be inexpensively manufactured, and the process cost for these components can be kept low. The substrate in this case constitutes the carrier for discrete components and ICs.
It is particularly preferred that the substrate of insulating material comprises Al2O3, glass, or Al2O3 with a planarizing layer of glass or of an organic material.
These materials are compatible with the thin-film technology and have an acceptable surface roughness. Al2O3 is particularly suitable as a substrate on account of its mechanical stability and thermal conductivity.
It is furthermore preferred that a barrier layer is provided between the substrate and the first structured electrically conducting layer or between the substrate and the resistance layer.
Reactions with the dielectric as well as rough surfaces of the electrically conducting layers, which will lead to short-circuits of the capacitors or bad high-frequency properties, can be prevented by a barrier layer.
It is advantageous when the first and second structured electrically conducting layers comprise Cu, Al doped with Cu, Al doped with Mg, Al doped with Si, or Al doped with Cu and Si.
It is furthermore preferred that the resistance layer comprises NixCryAlz (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), SixCryOz (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), SixCryNz (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), CuxNiy (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61), or TixWy (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61).
These materials are structured after being deposited, for example by means of lithographic processes in combination with wet and dry etching steps, depending on the functions which the layers are to fulfill in the thin-film circuit.
It is furthermore advantageous that the dielectric comprises Si3N4, SiO2, SixOyNz (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), SixCryOz (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61), or Ta2O5.
All these materials have a relative dielectric constant xcex5r greater than 4 and thus enable high capacitance values combined with small dimensions.
It is preferred that the protective layer comprises an inorganic material.
The protective layer protects the subjacent layers against mechanical loads and corrosion by moisture.
It is furthermore preferred that the structured metallization comprises a base layer and a covering layer.
In this embodiment, the base layer acts as a nucleating layer for the electrochemical deposition of the covering layer of the structured metallization.
It is highly preferred that discrete components are provided on the side of the substrate opposed to the thin-film circuit.
This utilization of a wafer on both sides can further enhance the packing density.
The invention further relates to a method of manufacturing a module provided with a thin-film circuit on an insulating substrate with at least one passive component, whereby
a first electrically conducting layer is deposited on a substrate and structured,
a dielectric is deposited on the first structured electrically conducting layer,
a second electrically conducting layer is deposited on the dielectric and structured,
a protective layer is provided on the second structured electrically conducting layer,
the dielectric and the protective layer are structured,
at least one contact hole passing through the module is created, and
a structured metallization is provided over the module and the contact hole.
In a particularly preferred embodiment, a first step is that a barrier layer is deposited on the substrate.
In an especially preferred embodiment, a resistance layer is first provided on the substrate or on the barrier layer and is structured.
It is furthermore preferred that the contact hole is created as a first step or after the provision of the protective layer.
Depending on the manufacturing process, the contact hole may be created after the protective layer has been provided, or already before the conductor strips and passive integrated components are provided by means of thin-film techniques.
It is preferred that, for the manufacture of the structured metallization, first a base layer is deposited over the module and in the contact hole,
then a layer of photoresist is deposited on the base layer and is structured in accordance with the desired structure of the metallization,
a covering layer is deposited on the base layer, and
the photoresist and certain portions of the base layer are removed.
The invention also relates to a thin-film circuit on a substrate of an insulating material provided with at least one passive component, which component comprises at least
a first structured electrically conducting layer,
a dielectric,
a second electrically conducting layer,
and provided with a protective layer,
with at least one contact hole which passes through the substrate, and
with a structured metallization which covers the protective layer and the contact hole.
The invention will be explained in more detail below with reference to five Figures and three embodiments.